Nat. Hazards Earth Syst. Sci., 11, 309–321, 2011
www.nat-hazards-earth-syst-sci.net/11/309/2011/
doi:10.5194/nhess-11-309-2011
© Author(s) 2011. CC Attribution 3.0 License.
Natural Hazards
and Earth
System Sciences
Economic motivation of households to undertake private
precautionary measures against floods
H. Kreibich1 , S. Christenberger2 , and R. Schwarze2,3
1 Helmholtz
Centre Potsdam German Research Centre for Geosciences (GFZ), Section Hydrology, Potsdam, Germany
of Innsbruck (UIBK), Faculty of Economics and Statistics, Innsbruck, Austria
3 Climate Service Center – CSC, Hamburg, Germany
2 Leopold-Franzens-University
Received: 5 May 2010 – Revised: 2 November 2010 – Accepted: 11 November 2010 – Published: 3 February 2011
Abstract. Flood damage is on the increase due to a combination of growing vulnerability and a changing climate. This
trend can be mitigated only through significantly improved
flood risk management which, alongside the efforts of public
authorities, will include improvements in the mitigation
measures adopted by private households. Economically
“reasonable” efforts to self-insure and self-protect should be
expected from households before the government steps in
with publicly-funded relief programmes. To gain a deeper
understanding of the benefits of households’ precautionary
measures, telephone interviews with private home owners
were conducted in the Elbe and Danube catchments in
Germany after the floods of 2002 and again after the floods
in 2005 and 2006. Only detached, solid single-family
houses were included in this study, which is based on
759 interviews. In addition, market-based cost assessments
were solicited based on a “model building”.
Expert
interviews and a literature review – including catalogues and
price lists for building materials and household appliances –
were used as back-up information for the cost assessments.
The comparison of costs and benefits shows that large
investments, such as building a sealed cellar, are only
economically efficient if the building is flooded very
frequently, that is, if it is located in a high flood risk area.
In such areas it would be preferable in economic terms
not to build a new house at all – or else to build a house
without a cellar. Small investments, however, such as oil tank
protection, can prevent serious damage at low cost. Such
investments are still profitable even if the building is flooded
every 50 years or less on average. It could be argued that
these low-cost measures should be made mandatory through
Correspondence to: H. Kreibich
(kreib@gfz-potsdam.de)
the enforcement of building codes. Financial incentives
built into insurance contracts coupled with limits set on
governmental relief programmes would provide an economic
motivation for people to invest in precautionary measures.
1
Introduction
Recent floods in Germany have caused high economic
damages. For example, the 1993 and 1995 floods in the
Rhine catchment area caused total damages of 810 million C,
the 1997 flood on the Odra river lead to damages of
330 million C, the Whitsun flood of 1999 in the Danube
catchment caused damages of 412 million C, the damages
caused within Germany by the extreme flood event of
August 2002 in the Elbe and Danube catchment amounted
to 11.6 billion C (Kron, 2004), while the August 2005 flood
in the Danube catchment resulted in losses of 189 million C
in the federal state of Bavaria alone (LfU Bayern, 2006).
The 2006 flood in the Elbe catchment caused damages
of approximately 100 million $ (Munich Re, 2009). The
amount of damages arising from the 2010 flood in the Oder,
Neisse and Elbe catchments in Germany has not yet been
calculated. It is expected that flood damages will rise due to
a combination of an increase in vulnerability, mainly trough
wealth accumulation in flood plain areas, changes in the
terrestrial system, e.g., land cover changes, river regulation
and a changing climate (e.g., Kundzewizc et al., 2005;
Crichton, 2008). A variety of conceptions and definitions
of “vulnerability” exist and there is no widely agreed
understanding of this term within the academic community
(Thywissen, 2006). This study adopts the natural sciencesoriented conception which defines risk as hazard multiplied
by vulnerability (e.g., UNDP, 2004), where vulnerability
Published by Copernicus Publications on behalf of the European Geosciences Union.
310
comprises two elements: exposure and susceptibility (Merz
and Thieken, 2004; Department of Human Services, 2000).
Consequently, a significant cause of rising flood damages are
increased house values as well as an increase in residential
and commercial developments in flood-prone areas, leading
to greater exposure for private households. In industrialised
countries, this trend is due to the growing attraction of living
near waterfronts, an efficient transport infrastructure and the
proximity of urban developments to flood risk areas. In
Germany, for example, communities with more than 5,000
inhabitants are twice as likely to be located near a river
(Borchert, 1992). Additionally, climate change may also be
responsible for an increase in flood damages in some regions.
In a Germany-wide study, Petrow and Merz (2009) identified
spatially and seasonally coherent trend patterns for the period
1951–2002 and suggested that the observed changes in flood
behaviour were climate-driven. In contrast to this, Mudelsee
et al. (2003, 2004) identified a decrease in winter flooding in
their analysis of long-term discharge records at the Dresden
gauge on the Elbe river, while summer flooding showed no
trend at all. On the basis of existing empirical trend studies
and scenario-based simulation studies, it must be concluded
that flood hazards are currently changing and that larger
changes are likely in the future. However, it is difficult to
establish a precise estimate of the impact of climate change
on extreme flood events (e.g., Smith, 1999; Schreider et
al., 2000; Hall et al., 2005; Svensson et al., 2006). At
present and with regard to the near future, the observed
and projected significant increase in flood damages is driven
largely by social factors, specifically increased exposure
(Barredo, 2009; Feyen et al., 2009; Hall et al., 2003).
The trend towards increasing flood damages can be
mitigated only through significantly improved flood risk
management which, in addition to efforts undertaken
by public authorities such as technical flood protection
measures and increased natural retention, will also include
improvements in the mitigation efforts adopted by private
households (Hayes, 2004; Wynn, 2004). Risk reduction
activities by individuals include precautionary measures
taken in and around exposed buildings, preparatory measures
such as collecting information about flood risk and flood
protection, participation in neighbourhood help, or buying
flood insurance. The following precautionary measures,
relating specifically to buildings, serve significantly to
mitigate damages in flood-prone areas (ICPR, 2002; ABI,
2003; Kreibich et al., 2005):
– building without a cellar,
– adapting the building structure,
– protecting properties using water barriers,
– safeguarding from hazardous substances, e.g., preventing oil contamination.
Nat. Hazards Earth Syst. Sci., 11, 309–321, 2011
H. Kreibich et al.: Economic motivation of households
Buildings without cellars are generally less expensive to
construct and are less affected by flooding, particularly in
cases where only low water levels occur, e.g., during groundwater flooding (Kreibich and Thieken, 2008). However, they
also entail opportunity costs in the form of lower housing
quality. Building a structurally flood resistant house, e.g.,
using a specially stabilised foundation to protect against
drift or buoyancy (i.e., lifting force) or sealing the cellar to
make it waterproof, implies a considerable outlay. Moreover,
these measures may fail, especially during extreme flood
events (MURL, 2000). Steel frame and brick buildings
tend to be less susceptible to collapse than other materials,
and waterproof drywalls will hold up over extended periods
of heavy inundation (USACE, 1996). Generally speaking,
improving the stability of a building mitigates the damage
caused by buoyancy, water pressure and erosion, and may
prevent free-standing elements from being washed away.
Mobile water barriers are another way to protect properties
against inundation, but in order to be effective they need a
prior flood warning and time to be set up. The effectiveness
of sandbag barriers also depends on the number of rows
and the duration of the flood (Reeve and Badr, 2003). A
detailed description of alternatives to non-reusable sandbags
is provided by Bowker (2002). A further important measure
is to ensure the secure storage of oil and other hazardous
substances, e.g., in flood-proof fuel oil tanks (ICPR, 2002).
Tanks may float when the flood water level rises, and
they may also be damaged by water pressure. Containers
must, therefore, be tested to ensure that they are secure
against buoyancy, and all openings (ventilation fittings, filler
plugs) must have watertight closures. Damage from oil
contamination is often not confined to a person’s own home,
but may also affect neighbouring buildings. In Germany, the
federal states have laws stipulating that oil heating systems,
including oil tanks, have to be flood-proofed within flood
risk areas (e.g., VAwS-Baden-Württemberg, 2005; VAwSHessen, 2006; VAwS-Bayern, 2008). Other precautionary
measures available to individuals are described, for instance,
in Holub and Hübl (2008), BMVBW (2002), Environment
Agency (2003a, b), FEMA (1998a, b) and USACE (1995,
1996).
Taking precautionary measures, prior to any cost-benefit
calculus, demands self-reliant behaviour on the part of the
individuals potentially affected. Raschky (2008) highlights
the effects on human behaviour of the institutional framework and the incentives it sets. There are few laws (e.g.,
building codes) requiring homeowners to take precautionary
measures: most measures are voluntary (Heiland, 2002).
Previous studies have shown that experience of flooding is
a significant factor in motivating people to take voluntary
precautionary measures (Grothmann and Reusswig, 2006;
Siegrist and Gutscher, 2006, 2008; Thieken et al., 2007).
For instance, it has been shown by Smith (1981) and Wind
et al. (1999) that damage is reduced significantly only in
cases where people have had frequent and recent experience
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H. Kreibich et al.: Economic motivation of households
311
Table 1. Flood damage surveys: computer-aided telephone interviews with private households affected by flooding.
Characteristics
Date of survey:
Region(s):
Surveys
April and May 2003
August and September 2007
City of Dresden
Flood(s):
2002
2005 and 2006
1967–2007
Number of households
interviewed:
1697
461
454
615 (472)
113 (97)
31 (30)
Thieken et al. (2007)
Kreibich and Thieken (2008),
Kreibich et al. (2010)
Kreibich et al. (2009)
Number of detached, solid
single-family
houses (with cellar):
Reference(s):
of flooding.
In addition to recent flood experience,
awareness of living in a flood-prone area seems to be
another decisive factor in taking precautionary measures
at home (Kreibich et al., 2005). Moreover, people tend
to take private precautionary measures only if they are
informed of the possibility and believe in the effectiveness of
the measures described (Grothmann and Reusswig, 2006).
Ultimately, from an economic point of view, individuals
need financial incentives before they will invest in selfprotection. Such incentives can be provided either through
appropriately worded insurance contracts (Kleindorfer and
Kunreuther, 1999; Botzen et al., 2009; Holub and Fuchs,
2009) or else through government finance schemes or aid
geared towards enhancing self-reliance. The efficiency of
spending, measured by the cost-benefit ratio, is an important
benchmark for establishing what constitutes “reasonable”
self-protection measures for households engaging in flood
risk mitigation efforts. The objective of this study is to
quantify specifically the benefits and costs of precautionary
measures at household level and to analyse how this
knowledge ties into people’s economic motivation to take
precautionary measures against floods. Only the mitigation
of direct economic losses is taken into account; the potential
effects of precautionary measures on indirect and intangible
damages are not addressed.
2
November and December 2006
Elbe and Danube catchments in Germany
Data and methods
In order to discover the benefits of private precaution in
terms of averted flood damages, telephone interviews were
conducted with private households in the Elbe and Danube
catchments in Germany after the floods of 2002 and again
after the floods of 2005 and 2006 (Thieken et al., 2007;
Kreibich and Thieken, 2008; Kreibich et al., 2010) and,
particularly, in the city of Dresden in August and September
2007 (Kreibich et al., 2009; Table 1). Lists were compiled
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of all the streets affected with the help of information
from local authorities (e.g., personal communication with
the administrative districts affected and with the city of
Dresden), flood reports or press releases, as well as with the
help of flood masks derived from radar satellite data (DLR,
Centre for Satellite Based Crisis information, www.zki.caf.
dlr.de). This provided the basis for generating buildingspecific random samples of households. Computer-aided
telephone interviews were conducted using the VOXCO
software package (www.voxco.com). The SOKO institute
for social research and communication (www.soko-institut.
de) conducted the interviews in April and May 2003 and in
September 2007. The Explorare market research institute
(www.explorare.de) conducted the interviews in November
and December 2006. In most cases, the person in the
household with the best knowledge of the flood damage was
interviewed. The first phase of the survey after the 2002
flood resulted in 1697 completed interviews. The second
phase in 2006 resulted in 461 interviews, and the survey in
the city of Dresden resulted in 454 completed interviews with
private households affected by flooding (Table 1). All the
questionnaires addressed, among other things, the following
topics: precautionary measures, flood parameters (e.g.,
contamination, water level), building characteristics and
flood damage to buildings and contents. Building damage
included all costs associated with repairing the damage
to the building structure, such as plastering, replacing
broken windows and repairing the heating system. Contents
damage included all costs incurred through repairing or
replacing damaged contents, such as domestic appliances,
telephone and computer systems and furniture.
The
questionnaire contained detailed questions addressing not
only total damage but also the area affected per storey,
the damage ratio, the type and amount of the most
expensive item damaged, and the type and costs of all
building repairs and all expensive domestic appliances
affected. This generated the most accurate information
Nat. Hazards Earth Syst. Sci., 11, 309–321, 2011
312
H. Kreibich et al.: Economic motivation of households
Table 2. Model building for costing.
Building type
Detached, solid
single-family house with
and without cellar
Property area (./. river adjacent)
Floor plan
Cellar area
750 m2 (10 m)
10 m × 14 m
65 m2
Thickness of base plate
Thickness of exterior walls
Thickness of cellar ceiling
Ceiling height
Cellar windows
Soil properties
25 cm
25 cm
20 cm
2.50 m
4
Clay
possible about the extent of damage, avoiding a strategic
response bias. Since many people claimed their damages
either from government funds or from their insurers, the
damage estimates are believed to be reliable. This was also
confirmed by a comparison of the damage data collected after
the 2002 flood with official damage data from the Saxon
Bank of Reconstruction (Sächsische Aufbaubank), which
was responsible for administering governmental disaster
assistance after the 2002 flood in the federal state of Saxony
(Thieken et al., 2005).
Only detached, solid, single-family houses were included
in this analysis of the benefits and costs of private precautionary measures. This selection resulted in 759 datasets
(Table 1). The homes’ median total area was 140 m2 (mean:
157 m2 ) and the median area of the surrounding plot was
750 m2 (mean: 1033 m2 ). Of these buildings, 599 had a
cellar and 160 were built without a cellar. The median cellar
area was 65 m2 (mean: 68 m2 ). These median values were
used to develop the “model building” for cost calculations
(Table 2). The buildings without a cellar were taken into
account only for the purpose of investigating the measure
“building without a cellar” (Sect. 3.2.1); for all the other
measures, only the single-family homes with a cellar were
analysed.
Drawing on the approach used by Kreibich et al. (2005),
damage reduction due to precautionary measures was
assessed by comparing actual damage cases where the
specific measure was taken with cases where the specific
measure was not taken, regardless of other measures. Cases
of damage where only the cellar was affected were separated
from the cases where the ground floor was also affected, in
order to take into account the severity of the inundation.
The cost calculations were based on the following “model
building”: a detached, solid single-family house with a total
area of 140 m2 and a cellar area of 65 m2 , located on a plot
of 750 m2 (for details see Table 2).
Nat. Hazards Earth Syst. Sci., 11, 309–321, 2011
Cost calculations were made on the basis of precautionary
measures being implemented during the construction phase,
i.e., the cost figures are for new buildings only. The cost
calculations are based on tendered construction bids, expert
interviews and a literature review, including catalogues and
price lists for building and household appliances. The
economic efficiency of the measures is calculated by means
of a benefit-cost ratio, where the benefit of a measure during
its total life-time is related to its total costs, including
investment and maintenance. A benefit-cost ratio above
one means that the benefits are greater than the costs and
the measure is efficient. Since benefits and costs occur at
different times, they are homogenised with an interest rate for
a common reference date (here the end date). Two interest
rates are used here: 3%, which is recommended for flood
protection measures by the German Working Group on water
issues of the Federal States and the Federal Government
(LAWA, www.lawa.de), and 4%, which is the long-term
market rate.
Benefit-cost ratios are calculated for two different water
depths, namely, flood situations where only the cellar
is affected and situations where the ground floors are
also affected. Additionally, three different hazard zones
(flood frequencies) are taken into account: buildings which
are affected by flooding once a year, buildings which are
affected once in 10 years and buildings affected once in
50 years.
3
3.1
Results and discussion
Economic motivation behind households’
precautionary measures
From a microeconomic point of view, households’ decision
to self-protect against risky events is an optimisation
calculation. Ehrlich and Becker (1972) were the first
to formalise this decision in an abstract model setting.
Transposed into an environment of natural risks, this model
would appear as depicted in Fig. 1. Figure 1 shows a
household’s decision to utilize wealth in different states of
nature – with and without a natural hazard occurring. Let W1
denote the “state of nature” without flooding and let W2 be
the “state of nature” where the damage-causing natural event
occurred. Wealth can be shifted between states of nature
by means of precautionary measures taken. For example,
the (efficient) amount of private precaution (X∗ ) can be
seen as a spending of wealth in the “state of nature” of no
flooding (W1 ) into the “state of nature” of a flood occurring
(W2 ). The household is saved from damages in state 2
(flooding) by a spending of wealth in state 1 (no flooding) for
precautionary purposes. The efficient shift of wealth between
states of nature – or, in other words, the efficient spending on
precaution (X∗ ) – is defined by the damage avoided (L-L∗ )
relative to the spending of X∗ . Let W be the wealth that is
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H. Kreibich et al.: Economic motivation of households
313
W2 (with damage)
W
X*
S
I4
C
I3
L*
Governmental relief conditional upon “reasonable”precaution
B
W – L*-X*
Schroeder -Rule of (full) compensation
I2
W– L
A
I1
W1 (without damage)
W – X*
W
Fig. 1. Basic economic model of precaution and governmental relief relating to damages caused by natural hazards.
available to the household in both states of nature (say, its
annual income). X∗ is a spending of wealth in the “state of
nature” of no flooding (W1) to protect wealth in the “state of
nature” of a flood occurring (W2). It mitigates the damages
which would occur without any private precaution (L) to the
level of flood protection (L∗ ). Thus, the household achieves
a state of wealth of W-L∗ -X∗ in the “state of nature” of a
flood occurring. This is an improvement to the situation
without precaution (W-L). For this, the household has to
spend precautionarily X∗ , i.e., it has to accept a lower level of
wealth (W-X∗ ) in the “state of nature” of no flooding as well.
The efficient substitution of wealth in the situation without
damages to the situation with damages is shown in Fig. 1
as the transition from point A to point B. Thus, the curve
through A and B shows the possibilities of transforming
spending for precaution into saved damages (transformation
curve). The ultimate choice of precautionary measures
taken by the household is made according to the goal of
maximizing household utility (U). The achievable levels of
utility are depicted by the convex indifference curves, which
could be seen as level curves of utility. Indifference curves, in
fact, mark combinations of wealth in both “states of nature”
(with and without flooding), which allow the same level of
utility (U). Therefore, higher indifference curves show higher
levels of utility, i.e., U(I3 ) > U(I2 ) > U(I1 ).
Obviously, the efficient amount of precaution (X∗ ) raises
the utility of households (from U(I1 ) to U(I2 )). However,
a misplaced promise of complete governmental relief after
natural disasters – as had been given, for example, by
former German Chancellor Schroeder after the 2002 flood
on the river Elbe in his aid policy guidance ‘that nobody
shall be worse off after the flood – raises recipients’ utility
levels to a higher level still, U(I3 ), while at the same time
disincentivising any precautionary efforts and any self-reliant
www.nat-hazards-earth-syst-sci.net/11/309/2011/
behaviour by the population potentially affected (in the
sense of Raschky, 2008). An incentive-oriented way of
equalising the wealth in both states of nature (with and
without flooding) would be to restrict governmental relief
to an amount (L∗ ) reflecting an efficient level of precaution
(X∗ ) or, in legal terms, making governmental aid conditional
upon “reasonable” efforts by private households to selfprotect. In order to implement such “incentive-oriented”
policies as a means of economically motivating precaution,
the regulator needs some empirical estimates of the costs and
benefits of private precaution. Benefit-cost ratios of private
precautionary measures generally also come into play when
banks are involved in the financing of any such measures.
3.2
Benefit from precautionary measures
Precautionary measures applied to private homes are
believed to be effective mainly in areas with frequent, smallscale floods (ICPR, 2002). However, many precautionary
building measures significantly reduced the flood damage
even during the extreme flood event of August 2002 in the
Elbe catchment (Kreibich et al., 2005).
3.2.1
Building without a cellar
Constructing a single-family house without a cellar may
be an efficient precautionary measure in flood-prone areas,
as buildings without cellars are generally damaged less by
flooding. Such homes suffer no damages when homes with
cellars are affected by low flood water. Thus, the average
building damages of 14 382 C and the average contents
damages of 9091 C of single-family houses with cellars
could be avoided completely in these cases (Fig. 2). In cases
with higher levels of flood water, where the ground floors
were additionally affected, the building and content damages
Nat. Hazards Earth Syst. Sci., 11, 309–321, 2011
H. Kreibich et al.: Economic motivation of households
20000
10000
5000
0
15000
10000
5000
20000
15000
10000
5000
25000
contents loss [€]
20000
25000
contents loss [€]
25000
15000
cellar onlycellar
affected
only affected
cellar onlycellar
affected
only affected
25000
building loss [€]
building loss [€]
314
0
0
with cellar with cellar
40000
20000
0
80000
60000
40000
20000
without cellar
without cellar
100000
80000
60000
40000
20000
0
0
with cellar with cellar without cellar
without cellar
120000
contents loss [€]]
60000
100000
5000
cellar and cellar
ground
floor
affected
and
ground
floor affected
120000
contents loss [€]]
80000
building loss [€]
€]
building loss [€]
€]
100000
10000
with cellar with cellar
120000
significant difference
significant difference
15000
0
without cellar
without cellar
cellar and ground
floor
affected
cellar and
ground
floor affected
120000
20000
significant significant
difference difference
100000
80000
60000
40000
20000
0
with cellar with cellar
without cellar
without cellar
Fig. 2. Differences in building and contents damages between buildings with or without cellars, separated into cases where only cellars were
affected and cases where ground floors also were affected (bars = means, points = medians and 25–75% percentiles, significant differences
between the cases with/without cellar are indicated).
were also significantly reduced on average by 23 904 C and
by 4419 C, respectively, where the single-family houses were
constructed without a cellar compared with the ones with a
cellar. The ICPR (2002) states that building without a cellar
can reduce flood damage in the residential sector in Germany
by between 3000 C and 6000 C. A study conducted after
the extreme flooding in 2002 reported a significant average
reduction of the damage ratios for buildings by 24% and
for contents by 22% in cases where only the ground floor
was affected in comparison with additional cellar damage
(Kreibich et al., 2005).
3.2.2
Adapting the building structure
The precautionary measure of building flood-proof adaptations into the structure includes, for example, the construction of an especially stable foundation or of waterproof,
sealed cellar walls with sealed piping. Unfortunately,
no separate information about these different methods
was acquired in the survey. One can only assume that
the buildings fitted with flood-proof adaptations that still
suffered losses in the cellar (when only the cellar was
affected) probably had a stable foundation but no waterproof,
sealed cellar. However, waterproofed tanking can also fail, or
else water can enter through unprotected cellar windows or
unsealed openings for utility pipes.
This measure showed a significant reduction in building
damage: by 5956 C on average if only the cellar was
affected, and by 20 473 C if the ground floor was affected as
well (Fig. 3). No significant contents damage reduction was
Nat. Hazards Earth Syst. Sci., 11, 309–321, 2011
achieved. Kreibich et al. (2005) also reported no impact on
contents damage from this measure but a mean reduction of
the building damage ratio by 24%. In fact, in areas with great
flood depth, this measure can be applied only to a limited
extent, as the risk of buoyancy (or lifting force) of the flood
water must be taken into account (Kelman and Spence, 2003;
Kreibich and Thieken, 2008). If flood waters rise to high
levels and the building is not protected against buoyancy, the
cellar must be partly or entirely flooded with clean water
in order to ensure stability. Thus the ICPR (2002) reports
a damage reduction potential of between 75% and 85% of
such structural building measures, albeit always dependent
on the need to flood the cellar with clean water to preserve
stability.
3.2.3
Water barriers
Domestic flood water barriers such as sandbags, mobile
flood walls and sealants for doors and windows are only
effective if they are able to withstand high water levels and
if their impact is not negated by permeable cellar walls or
openings for utility pipes. It is not surprising then, that in
the cases where only cellars were affected, flood barriers
showed no significant effect (Fig. 4). In the cases where
ground floors were additionally affected, flood water barriers
led to a significant average reduction in building damages
of 23 491 C. However, there was no significant impact on
contents damages (Fig. 4). The ICPR (2002) states that
if the flood water does not flow over the water barriers,
damage is potentially reduced by 60–80%. The remaining
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H. Kreibich et al.: Economic motivation of households
315
cellar onlycellar
affected
only affected
cellar onlycellar
affected
only affected
25000
25000
25000
20000
20000
25000
no significant
difference difference
no significant
5000
15000
10000
5000
0
0
15000
10000
5000
20000
contents loss [€]
10000
building loss [€]
building loss [€]
15000
contents loss [€]
significant significant
difference difference
20000
15000
10000
5000
0
0
adapted adapted
not adapted
not adapted
building structure
building structure
adapted adapted
not adapted
not adapted
building structure
building structure
cellar and cellar
ground
floor
affected
and
ground
floor affected
100000
cellar and cellar
ground
floor
affected
and
ground
floor affected
100000
100000
100000
80000
80000
80000
80000
60000
60000
60000
60000
40000
40000
40000
40000
20000
20000
20000
20000
0
0
0
0
contents loss [€]
no significant
difference difference
no significant
contents loss [€]
building loss [€]]
building loss [€]]
significant significant
difference difference
adapted adapted
not adapted
not adapted
building structure
building structure
adapted adapted
not adapted
not adapted
building structure
building structure
Fig. 3. The influence of flood adapted building structure on building and contents damages, separated into cases where only cellars were
affected and cases where ground floors were affected as well (bars = means, points = medians and 25–75% percentiles, significant differences
between the cases with/without adapted building structure are indicated).
15000
10000
5000
5000
0
0
20000
15000
10000
5000
no difference
significant difference
no significant
0
20000
0
not available
available available not available
water barriers
water barriers
80000
60000
40000
20000
0
no difference
significant difference
no significant
contents loss [€]
€]
20000
40000
contents loss [€]
€]
40000
60000
5000
100000
100000
significant significant
difference difference
building loss [€]]
building loss [€]]
60000
10000
and
ground
floor affected
cellar and cellar
ground
floor
affected
100000
80000
15000
not available
available available not available
water barriers
water barriers
and
ground
floor affected
cellar andcellar
ground
floor
affected
80000
20000
0
0
not available
available available
not available
water barriers
water barriers
100000
only affected
cellar onlycellar
affected
25000
contents loss [€]
10000
20000
contents loss [€]
15000
25000
no significant
no significant
difference difference
building loss [€]
building loss [€]
20000
only affected
cellar onlycellar
affected
25000
25000
80000
60000
40000
20000
0
not available
available available not available
water barriers
water barriers
Fig. 4. The influence of water barriers on building and contents damages, separated into cases where only cellars were affected and cases
where ground floors were affected as well (bars = means, points = medians and 25–75% percentiles, significant differences between the cases
with/without water barriers are indicated).
www.nat-hazards-earth-syst-sci.net/11/309/2011/
Nat. Hazards Earth Syst. Sci., 11, 309–321, 2011
316
H. Kreibich et al.: Economic motivation of households
damage depends mainly on the damage potential of cellars
and whether or not cellar walls are sealed and waterproofed
(ICPR, 2002). During the extreme flood event of 2002, many
of the water barriers that had been erected were overwhelmed
by the flood waters and, thus, had little to no effect. Still,
during this flood the damage ratio of buildings was reduced
on average by 29% for the cases where water barriers were
in place (Kreibich et al., 2005).
3.2.4
Prevent oil contamination
In the cases where no oil contamination occurred, building
damages were significantly lower on average: by 10 482 C if
only cellars were affected and by 26 447 C if ground floors
were affected as well (Fig. 5). Surprisingly, contents damage
was significantly reduced, by an average of 4984 C, only if
cellars alone were affected (Fig. 5). Generally speaking, oil
contamination can cause damage to buildings that is three
times as great on average as without contamination and in
particular cases it can even lead to total damage (Egli, 2002).
For example, during the Whitsun flood of May 1999 in
the region of Kelheim, Bavaria in the south of Germany,
the mean damage to buildings amounted to 15 622 C. In
cases where there was additional oil contamination, the mean
damage increased to 52 886 C (Deutsche Rückversicherung,
1999). As oil contamination is not confined to those
buildings where a domestic oil tank collapses or leaks, but
may also cause damage to other properties, oil tanks in flood
risk-areas should be flood-proofed even if the individual costbenefit ratios are below one.
3.3
3.3.1
Cost-benefit of precautionary measures
Building without a cellar
Building a (flood-proofed) cellar is generally cost-intensive
(as detailed in the next section). Thus, it seems reasonable
to construct buildings without a cellar in flood-prone areas,
particularly since buildings without cellars are also less
expensive to construct.
The costs of living without a cellar depend mainly on the
availability of alternative storage area. If there is enough
storage area in higher storeys, e.g., the attic, no costs are
incurred by this measure. In this case, building houses
without a cellar is always economically efficient, since only
benefits result (mitigated flood damages (Fig. 2), perhaps
lower construction costs). If alternative storage area needs to
be rented elsewhere due to a lack of space, opportunity costs
are incurred. Average rental prices for floor space provide
an estimate of these opportunity costs. Rental prices for
floor space are between 3 and 4 C m−2 (IHK Dresden, 2009)
depending on the location in the federal state of Saxony in
Germany. Since having “a cellar in one’s own house” can be
equated with being in a particularly attractive location, the
upper limit of 4 C m−2 is taken here. Thus, for a storage area
Nat. Hazards Earth Syst. Sci., 11, 309–321, 2011
of 65 m2 the alternative costs amount to 3120 C a year. Since
these costs are expenses incurred annually, interest charges
do not need to be considered.
Benefit-cost ratios are shown in Table 3. The construction
of residential buildings without a cellar and renting alternative storage space is an efficient precautionary measure in
high risk areas which are flooded once a year. However, in
the long run, it is more expensive than having waterproofed,
sealed cellar walls when a low interest rate (≤3%) applies
(Table 4). In lower risk areas it is more expensive to rent
alternative storage space than to accept the risk of rare flood
damages in the cellar (Table 3).
3.3.2
Waterproofed, sealed cellar walls – adapting the
building structure
There are two common methods for waterproofing cellar
walls: (a) constructions with a waterproof skin (bitumen
sealing); (b) waterproof concrete with concrete slabs and
waterproof interstices. Both have an average lifetime of
about 75 years based on expert judgement (city of Vienna,
personal communication, 2008), depending on the load.
Building a waterproofed cellar using a construction with
a waterproof skin (bitumen sealing) costs 465.10 C m−2 ,
according to the construction bids tendered (Alpine Bau,
personal communication).
These costs need to be
reduced by the costs which arise anyway (that is, if a
“normal”, not specifically waterproofed cellar is built): i.e.,
465.10 C m−2 minus 180 C m−2 , resulting in difference
costs of 285.10 C m−2 . Multiplying this figure by the 65 m2
of cellar floor gives rise to total costs for flood-proofing cellar
walls of 18 531.50 C. Given an average lifetime of 75 years,
annual costs are 4681.12 C or 2268 C, depending on the
choice of interest rate of 4% or 3%, respectively.
Building a cellar using waterproof concrete with concrete
slabs and waterproof interstices costs 505.00 C m−2 . Deducting the costs which arise anyway if a “normal” cellar
is built, the calculation is 505.35 C m−2 – 180.00 C m−2 =
325.35 C m−2 . For a cellar area of 65 m2 this results in total
costs of 21 147.75 C. Given an average lifetime of 75 years,
annual costs are 5341.99 C or 2588.18 C, depending on the
choice of interest rate of 4% or 3%, respectively.
The average benefit per flood event of building structure
adaptations, e.g., waterproof, sealed cellar walls by tanking
is 5956 C if only the cellar is affected, and 20 473 C if both
the cellar and ground floor are affected (Fig. 3).
The resulting benefit-cost ratios for the two different
constructions possible for waterproofed cellar tanking are
shown in Table 4 for two different water depths and
three different hazard zones (flood frequencies). For both
constructions, benefit-cost ratios are above one only for
frequent flooding once a year, regardless of the interest rate
selected.
www.nat-hazards-earth-syst-sci.net/11/309/2011/
H. Kreibich et al.: Economic motivation of households
317
Table 3. Benefit-cost ratios for the construction of residential buildings without a cellar.
Cellar only affected
Opportunity costs:
annual rental prices
Benefit per year
(see Fig. 2)
Benefit-cost ratio
3120 C
3120 C
3120 C
23 473 C
2347 C
469 C
7.52
0.75
0.15
3120 C
3120 C
3120 C
28 323 C
2832 C
566 C
9.08
0.91
0.18
Affected once a year
Affected once in 10 years
Affected once in 50 years
Cellar and ground floor affected
Affected once a year
Affected once in 10 years
Affected once in 50 years
Table 4. Benefit-cost ratios for the construction of waterproof, sealed cellar walls using tanking: (a) constructions with a waterproof skin
(bitumen sealing); (b) waterproof concrete tanking with concrete tanked slab and waterproof interstices.
Costs per year
i.r.∗ 4%
Benefit per year
i.r. 3%
(see Fig. 3)
Benefit-cost ratio
i.r. 4%
i.r. 3%
1.27
0.13
0.03
2.63
0.26
0.05
(a) waterproof skin (bitumen sealing) – cellar only affected
Affected once a year
Affected once in 10 years
Affected once in 50 years
4681 C
4681 C
4681 C
2268 C
2268 C
2268 C
5956 C
596 C
119 C
(a) waterproof skin (bitumen sealing) – cellar and ground floor affected
Affected once a year
Affected once in 10 years
Affected once in 50 years
4681 C
4681 C
4681 C
2268 C
2268 C
2268 C
20 473 C
2047 C
410 C
4.37
0.44
0.09
9.03
0.90
0.18
(b) concrete tanked slab and waterproof interstices – cellar only affected
Affected once a year
Affected once in 10 years
Affected once in 50 years
5342 C
5342 C
5342 C
2588 C
2588 C
2588 C
5956 C
596 C
119 C
1.11
0.11
0.02
2.30
0.23
0.05
(b) concrete tanked slab and waterproof interstices – cellar and ground floor affected
Affected once a year
Affected once in 10 years
Affected once in 50 years
5342 C
5342 C
5342 C
2588 C
2588 C
2588 C
20 473 C
2047 C
410 C
3.83
0.38
0.08
7.91
0.79
0.16
∗ i.r. = interest rate.
3.3.3
Mobile flood water barriers
Mobile water barriers are used in a similar way to sandbags to
prevent the intrusion of surface water during flooding. They
are especially advantageous, since they are only used when
necessary and are reusable. Purchasing a mobile barrier 1 m
in height, including the necessary support, costs 610 C per
m (www.hochwasserschutz.de). Given an average lifetime
of 20 years, annual costs of either 66.80 C or 55.10 C per
running metre arise, depending on the choice of interest rate
www.nat-hazards-earth-syst-sci.net/11/309/2011/
of 4% or 3%, respectively. For an average “model property”
of 750 m2 , 10 m of property length are estimated to be
adjacent to a river. Since mobile water barriers protect
against surface water only and are efficient only if their
impact is not negated by the presence of permeable cellar
walls, it is hardly surprising that they are only economically
efficient if the cellar and ground floor are affected by flooding
(Table 5). Cost-benefit ratios are positive (above one) for
flood frequencies of once in 10 years or more often.
Nat. Hazards Earth Syst. Sci., 11, 309–321, 2011
318
H. Kreibich et al.: Economic motivation of households
cellar onlycellar
affected
only affected
cellar only cellar
affected
only affected
5000
25000
0
20000
15000
10000
5000
60000
40000
20000
0
building loss
s [€]
building loss
s [€]
120000
80000
15000
10000
5000
20000
15000
10000
5000
0
without cont.
without cont.
with cont. with cont.
cellar and ground
floor
affected
cellar and
ground
floor affected
120000
120000
100000
100000
significant difference
significant difference
80000
60000
40000
20000
80000
60000
40000
20000
0
0
with cont. with cont.
25000
0
0
with cont. with cont.
100000
20000
significant significant
difference difference
contents loss [€]
10000
25000
significant difference
significant difference
30000
without cont.
without cont.
without cont.
without cont.
cellar and cellar
ground
floor
affected
and
ground
floor affected
120000
no significant
difference difference
no significant
contents loss [€]
15000
30000
contents loss [€]
20000
30000
contents loss [€]
25000
building loss [€]
building loss [€]
30000
100000
80000
60000
40000
20000
0
with cont. with cont.
without cont.
without cont.
Fig. 5. The influence of oil contamination on building and contents damages, separated into cases where only cellars were affected and cases
where ground floors were affected as well (bars = means, points = medians and 25–75% percentiles, significant differences between the cases
with/without contamination are indicated).
Table 5. Benefit-cost ratios for mobile water barriers.
Cellar and ground floor affected
Affected once a year
Affected once in 10 years
Affected once in 50 years
Costs per year
Benefit per year
Benefit-cost ratio
i.r.∗ 4%
i.r. 3%
(see Fig. 4)
i.r. 4%
i.r. 3%
668 C
668 C
668 C
551 C
551 C
551 C
23 491 C
2349 C
470 C
35.17
3.52
0.70
42.63
4.26
0.85
∗ i.r. = interest rate.
3.3.4
Preventing oil contamination by securing oil tanks
Oil tanks should be secured in all flood risk areas, not only
because of the potential economic damages to buildings
and other assets but also due to the risk of ecological
damage. The costs of doing so are 1009 C for a floodproofed oil tank with a volume of 1500 litres which is secured
against buoyancy (Fachgemeinschaft Ölwärme & Service,
2008). Given an average lifetime of an oil tank of 30 years
(Fachgemeinschaft Ölwärme & Service, 2008), annual costs
arising are roughly either 109 C or 82 C depending on the
interest rate selected of 4% or 3%, respectively. Securing oil
tanks is a measure that consistently shows a positive benefitcost ratio above one (Table 6), in contrast to large, expensive
construction measures such as waterproofing cellar walls by
tanking (Table 4).
Nat. Hazards Earth Syst. Sci., 11, 309–321, 2011
4
Conclusions
The rise in flood damages calls for significantly improved
flood risk management and greater self-reliance on the
part of private households, including greater involvement
in mitigation measures. Economically “reasonable” efforts
to self-insure and self-protect can be expected from
households in the face of rising damages, alongside increased
protection by public authorities and governmental relief
programmes. This study has looked at the efficiency of
selected precautionary measures taken by private households
against floods. To summarise the findings: large investments,
e.g., waterproofed cellars, are economically “reasonable”
if the building is located in a high risk area. Small
investments, e.g., securing oil tanks, are economically
“reasonable”, even if the building is flooded only once every
50 years. The policy-related conclusions arising from these
www.nat-hazards-earth-syst-sci.net/11/309/2011/
H. Kreibich et al.: Economic motivation of households
319
Table 6. Benefit-cost ratios for securing oil tanks.
Costs per year
i.r.∗ 4%
Benefit per year
i.r. 3%
(see Fig. 5)
Benefit-cost ratio
i.r. 4%
i.r. 3%
141.89
14.19
2.83
188.61
18.87
3.77
242.63
24.27
4.85
322.52
32.26
6.45
Cellar only affected
Affected once a year
Affected once in 10 years
Affected once in 50 years
109 C
109 C
109 C
82 C
82 C
82 C
15 466 C
1547 C
309 C
Cellar and ground floor affected
Affected once a year
Affected once in 10 years
Affected once in 50 years
109 C
109 C
109 C
82 C
82 C
82 C
26 447 C
2645 C
529 C
∗ i.r. = interest rate.
findings are that legislation should be in place to prevent
the construction of buildings in flood risk areas and should
make “reasonable” precautionary measures mandatory for
people already living in such areas. The motivation of private
households to take such measures could be enhanced via
financial incentives, e.g., by making governmental assistance
for damages conditional upon “reasonable” precautions, or
by reducing premiums as a part of home insurance contracts
(Holub and Fuchs, 2009). Finally, it appears reasonable to
speculate that as the costs of commonly applied measures
fall due to mass production, more precautionary measures
will become economically efficient.
Acknowledgements. This research was undertaken partly within
the framework of the MEDIS project (Methods for the Evaluation
of Direct and Indirect Flood Losses), funded by the German
Ministry of Education and Research (BMBF) (No. 0330688)
and partly within the framework of the “Climate-proof flood risk
management” project supported by the Dutch research programme
Knowledge for Climate (Theme 1). The survey in 2006 was also
undertaken as part of the MEDIS project. The survey after the 2002
flood was undertaken under the auspices of the German Research
Network Natural Disasters (DFNK) and was funded by Deutsche
Rückversicherung AG and BMBF (No. 01SFR9969/5). The survey
in the city of Dresden was conducted within the MULTISURE
project (Entwicklung multisequenzieller Vorsorgestrategien für
grundhochwassergefährdete urbane Lebensräume), funded by
BMBF (No. 0330755).
Edited by: L. Ferraris
Reviewed by: S. Fuchs and another anonymous referee
www.nat-hazards-earth-syst-sci.net/11/309/2011/
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